A conventionally proposed drivable distance calculation device estimates the drivable distance based on a remaining capacity of an in-vehicle battery of an electric vehicle. When the destination or route is set in a navigation system, the calculation device estimates the drivable distance by comparing the consumption of the battery with the remaining capacity of the battery for each link included in the route to the destination or the set route (see Japanese Patent Application Laid Open Publication No. 2006-115623). The calculation device of Japanese Patent Application Laid-open Publication No. 2006-115623 cannot estimate the drivable distance when the route is not set. To estimate the drivable distance when the route is not set, the drivable distance may be calculated based on the consumption of the battery at the link where the vehicle is currently traveling or based on the consumption of the battery which is indefinitely predicted from daily driving.
In the former case, since the drivable distance is estimated based on the battery consumption in the link at the time of the estimation, the instantaneous accuracy of the estimated drivable distance is high but the estimated drivable distance can change considerably each time the vehicle travels to a different link. If the drivable distance is reduced suddenly, the driver is likely to have a feeling of anxiety. If the drivable distance is increased suddenly, the driver is likely to rely on the estimated drivable distance excessively. In the latter case, the drivable distance does not change significantly, but its problem in accuracy simply increases the risk of running out of electricity when the remaining capacity of the battery becomes small.